Questions about programmable switches

[Stormin Mormon]

Picture of receptacle:

[Stormin Mormon]

I'm also not great at pulling wires. However, I think you'll find one of the cloth wraps is hot, the other is neutral. Least, that's what I've always found.

[Stormin Mormon]

How would run any 110VAC or 120 VAC device, and not have a neutral? Don't think that's ever been done.

[Stormin Mormon]

So the programmable switch uses the load as a neutral for the timer circuit? That's interesting.

[Retired]

Chris, Chris,

The switch box has no neutral available. Not the house. See this diagram

[Stormin Mormon]

Thanks, that sure makes things a LOT more clear. The diagram is a big, big help.

[Ralph Mowery]

I put a quote mark around the 'fake neutral' to try and indicate it is not a true neutral. The hot wire with 120 volts on it goes to the switch. The wire leaving the switch goes through the load and back to the neutral. That is the reason for the minimum load. With no load , there is no return for the power and the switch will not work.

When the load is powered up there are a couple of volts dropped across the switch to keep it powered up.

[philoÂÂ]

In a switch box there would not normally be a neutral wire... there would be a (black) "hot" and the other wire is the one going to the bulb.

It would be against electrical code to use the ground wire (green) as a return.

[Stormin Mormon]

Volt dropping: "Hey, did you know that I'm distantly related to DC? You look great in that insulation. Black is really your color. You're hot. Love the way you keep your split ends under a wire nut like that. Millie Amp says hi. She's got great potential. You do know that Edison and I were best friends?"

[trader4]

It's an outlet that you plug things into.

If the box has no neutral, then there is no code compliant way to make the switch that requires it work. The issue is that a programmable switch needs to be powered somehow. That could be by a battery, through the hot and neutral, or by using the load circuit. The latter is why the other switch has a minimum load of 25W. Without some kind of minimal load for a small current to flow through and power the switch even when it's off, it would have no power. That small current flows through the bulb when off and it's enough for thw switch, but so tiny it won't light the bulb at all.

[Jennifer Murphy]

The minimum it said it needed was actually 40W.

Does the switch really draw 40W for its own use? That seems like a lot for a small electronic circuit. It does have an LED screen that could be on Hi all the time depending on user settings. I have mine set to dim after 8 seconds.

With a regular toggle switch, off is an open circuit (no current flowing), right?

[Ralph Mowery]

With a regular on/off switch, no current will flow when off if it is operating properly.

The programmable switch has to have a connection through the load back to the neutral of the AC power. It will take a certain ammount of a load to provide that. Some loads like the new CFL or LED bulbs may not work as loades either.

The programmable switch doen not draw 40 watts , but much less maybe a watt or two or even less. If it drew much power at all and you put an old filiment light bulb as the load, it would glow maybe a dull red. I doubt you would see anykind of glow at all with the switch in the off position even though a small ammount of current will be flowing.

A 60 watt bulbs takes about 1/2 of an amp or 500 ma. On dry skin you can feel about 1 or 2 ma. Get up to around 50 ma and it can be painful. Much more and maybe death.

[trader4]

No, it draws negligible amount of power. If it drew

40W the box would over heat. It's just that with no neutral, the switch winds up getting it's power in series with whatever the load is. With too small of a load, the switch can't get the necessary voltage/current that it needs.

That seems like a lot

Yes. And with one of those other prog switches that use a neutral, the tiny current to power the switch electronics is flowing from the hot, throught the switch, to the neutral. So, with those the line going to the light is open too. With the switches that don't require a neutral, with the switch off, you still have that tiny current flowing from hot, through switch, through load, then to neutral at the load.

[Jennifer Murphy]

If the switch obnly needs a fraction of a watt to operate, why does it say that the load must be at least 40W? Why couldn't it get ebnough power with a 5W bulb as the load. 5W is much larger than a fraction of a watt.

I should have paid closer attention in freshman physics.

[jamesgang]

The switch is in series with the load, in this case a light bulb. So if yo u only have a 5 watt bulb the current flow would be too low to generate the needed voltage at the switch. Read about resistors in series if you are r eally interested in the physics and consider one of the resistors the switc h and the other, the light bulb.

[Tony Hwang]

Hi, Sounds like it is SS type switch like SCR. Without proper load creating enough current flow the gate can't trigger to make the switching device close(conduct. Think in terms of electronics, not electric/mechanical. Read up on things like SCR, TRIAC, DIAC, DIODES, opto electric Darlington switch, etc. On the other hand some of those kinda switches always have residual current flow even if off state. Use that switch on CFL light, you will see it just dims when turned off.

[jamesgang]

f you only have a 5 watt bulb the current flow would be too low to generate the needed voltage at the switch. Read about resistors in series if you a re really interested in the physics and consider one of the resistors the s witch and the other, the light bulb.

That's not the issue.

The timer uses the line through the load to operate it's clock because it h as no neutral. If the load is missing or not enough the clock doesn't work properly. 5 watts is plenty of load for a scr or triac.

[Tony Hwang]

Hmm, So, I = P/E 5/120~~ 42 mA. Not much of a current. If there is no neutral Is it open circuit? I don't get it. >>>(switch)>>>(load)>>>> where does this line end up? No neutral?

[trader4]

you only have a 5 watt bulb the current flow would be too low to generate t he needed voltage at the switch. Read about resistors in series if you are really interested in the physics and consider one of the resistors the swi tch and the other, the light bulb.

+1

Another simpler way of looking at it is the thermostat needs a path to a neutral. A 1000W load is a low resistance and closer to being directly connected to a neutral than a 5W load.

[trader4]

if you only have a 5 watt bulb the current flow would be too low to genera te the needed voltage at the switch. Read about resistors in series if you are really interested in the physics and consider one of the resistors the switch and the other, the light bulb.

it has no neutral. If the load is missing or not enough the clock doesn't work properly. 5 watts is plenty of load for a scr or triac.

It's plenty of current to run the clock/timer/lcd electronics in the programmable timer. How much current does it take to run a digital watch?

If there is no

When the switch is off, it relies on the path through the load, to the neutral, to complete the circuit. That's why the load has to be at least 40W, or whatever the number was.